(1) Field of the Invention
The present invention relates to a method for producing a heat exchanger having a flat metal tube with a plurality of fluid passageways and header pipes connected to opposite ends of the flat tube, and in particular, to a method for joining and connecting the header pipe to an end of the flat tube.
(2) Description of the Prior Art
As a typical heat exchanger having a flat metal tube with a plurality of fluid passageways therein and fluid inlet and outlet tubes connected to the flat metal tubes through header pipes on opposite ends of the flat metal tube, a serpentine-type heat exchanger is known in the prior art which is used for, for example, a refrigerant evaporator in an automotive air conditioning system, as shown in, for example, U.S. Pat. Nos. 4,350,025 and 4,353,224.
The serpentine heat exchanger comprises a flat metal tube formed in a serpentine-anfractuous shape to have a plurality of parallel portions spaced apart from one another. A plurality of corrugated fin units are disposed in spaces between adjacent ones of the parallel portions of the tube and are joined thereto by brazing. Header pipes are fixedly mounted on opposite ends of the flat tube, respectively, and an inlet tube and an outlet tube are connected to the header tubes, respectively.
In U.S. Pat. No. 4,353,224, only header pipes are shown at 3 and 4 in FIG. 1 of the drawing, while header pipes are shown at 3 and 5 in FIG. 5 of U.S. Pat. No. 4,350,025 which are integral with the inlet tube and the outlet tube, respectively.
In practical arrangement, header pipes are formed as different parts from the inlet and outlet pipes and are connected thereto.
The flat tube and the fin units are made of high heat-conductivity materials, such as aluminum alloys. Usually, the serpentine-anfractuous flat tube is made of an aluminum metal having 99 wt. % or more Al, for example, AA (Aluminum Association in U.S.A.) 1050 which comprises, by weight, 0.25% or less Si, 0.40% or less Fe, 0.05% or less Cu, 0.05% or less Mn, 0.05% or less Mg, 0.05% or less Zn, 0.03% or less Ti and 99.50% or more Al, or AA 3003 which comprises, by weight, 0.6% or less Si, 0.7% or less Fe, 0.05-0.20% Cu, 1.0-1.5% Mn, 0.10% or less Zn and the balance Al. The corrugated fin unit is made of an aluminum alloy brazing sheet which has a core metal of, for example, AA 3003 with a cladding of an aluminum alloy brazing filler metal, such as AA 4343, 4045 or 4047 (which comprises, by weight, 0.30% or less Cu, 5-13 % Si, 0.8% or less Fe, 0.15% or less Mn, up to 0.1% Mg, 0.20% or less Zn, up to 0.20% Ti, and the balance substantially Al).
The corrugated fin units of the aluminum alloy brazing sheet are assembled to the serpentine-anfractuous flat tube of the aluminum alloy, and thereafter, deposited into a brazing furnace. Thus, corrugated fin units are brazed and joined to the flat tube.
Header pipes are usually made of the aluminum alloy brazing sheet similar to the corrugated fin unit. The header pipes are assembled onto the flat tube before being deposited into the brazing furnace. Therefore, the header pipes are also brazed and joined to the flat tube simultaneously with brazing of the corrugated fin units to the flat tube.
Thereafter, the inlet tube and the outlet tube are connected to respective header pipes by, for example, TIG (Tungsten-inert gas) welding, while maintaining predetermined orientations of the tubes.
In brazing the header tubes to the flat tube in a condition wherein the header tubes are disposed at a level lower than the flat tube, the molten brazing filler metal flows down along the surfaces of the header pipes, and the brazing filler metal is not sufficiently fed to the connecting portions of the header pipes and the flat tube. As a result, a reliable joint of the header pipe and the flat tube is not obtained.
Furthermore, in the known production method, it is difficult to connect and join the inlet pipe and the outlet pipe to header pipes, respectively, while maintaining predetermined orientations of the tubes.